It is known to incorporate water repellant materials into hydratable cementitious materials such as cement pastes, masonry cements, mortars, and concrete to achieve a degree of moisture impermeability. A cementitious composition which is impermeable to water and dampness, ideally, may not require the application of externally applied moisture barriers such as bituminous coatings or waterproofing membrane laminates.
In U.S. Pat. No. 6,761,765 B2 (issued Jul. 13, 2004), Lu disclosed an emulsion admixture for imparting water repellant properties to cements. The admixture comprised a polymer, a surfactant, and hydrophobic material in the form of organic esters of aliphatic carboxylic acid. The polymer was preferably a latex polymer (e.g., styrene butadiene copolymer latex). The surfactant could include any surfactant capable of emulsifying the hydrophobic material, and most preferably was an ethoxylated nonylphenol. Lu theorized that mixing the emulsified hydrophobic material into the cementitious composition would evenly distribute it throughout the cementitious matrix as well as over its surface. This purportedly prevented water from entering and exiting porous cementitious structures such as blocks, pavers, and retaining wall units (See Col. 4, 11. 17-24).
Emulsified hydrophobic materials, however, were long known and used previously. For example, U.S. Pat. Nos. 3,865,601 and 3,885,985 disclosed additives comprising oil-in-water emulsions that contained a water-insoluble, water-repelling acid component (e.g., tall oil, an emulsifier (e.g., a salt of such an acid)) and a setting time retarding agent (e.g., sucrose). As explained in the background of U.S. Pat. No. 5,108,511, this additive was dispersible in water form so that the risk of overdosing could be minimized. Further, the additive was provided in a form that allowed additional optional components, such as air-entraining agents, to be included. An improved emulsion additive, as described in U.S. Pat. No. 4,375,987, further included an emulsion stabilizer (e.g., a glycol). The stabilizer, as is now well known, prevents oil-in-water emulsions from breaking down when exposed to freezing temperatures during shipping or storage. (See e.g., U.S. Pat. No. 5,108,511 at column 2, lines 11-23).
In U.S. Pat. No. 5,108,511, Wiegland observed that oil-in-water emulsions were unusable when they broke down. Even when stabilizers (such as glycol) were used in such aqueous systems, the emulsion could break down due to extreme temperature fluctuation and long term thermal cycling. Thus, for the express purpose of increasing workability, plasticity, and board life in mortar cement, Wiegland proposed an additive that comprised a salt of stearic acid (e.g., calcium stearate, aluminum stearate), a set retarding carbohydrate, an ethylenic glycol selected from mono-, di-, tri-, and tetraethylene glycols, and cellulose ether. The stearic salt was saponified by heating the stearic acid and lime powder.
The use of oil-in-water emulsions and saponified metal salts (e.g., calcium stearate) has been commercialized in the industry for some time. An emulsion-based, water-repellancy enhancer, added during the intergrinding process for making cement from clinker, is commercially available from Grace Construction Products, Cambridge USA, under the tradename HYDROPHOBE®. A calcium stearate suspension, provided in the form of finely ground calcium stearate powder, dispersed in an aqueous carrier, is commercially available from Grace under the tradename DARAPEL®.
To improve upon the prior art water repellency technology, the present inventors propose to avoid the use of aqueous emulsions or aqueous solvents.